I was having an issue when install the Prerequisites for a new install of SharePoint 2013, I was getting errors when trying to install the Microsoft Identity Extensions. Turns out you can download the standalone installer and to a manual command line install.
Run the command below to install and then the Prerequisite installer for SharePoint 2013 should continue on its merry way.
C:\Windows\System32>msiexec.exe /i “C:\foldername\MicrosoftIdentityExtensions-64.msi” /quiet /norestart
Where foldername is the name of the folder you have downloaded the file to. Happy Sharepointing !